If you read a lot about environment and development, one word and phrase that you often come across is Gaia and “the Gaia hypothesis,” a strange and wonderful idea that is at once odd and yet seemingly obvious. This theory proposes that the earth, with all its geological and geographical features, with its oceans and atmosphere, with its uncountable number of plants, animals, bacteria and viruses, actually functions like a single organism that maintains internal conditions necessary to keep itself stable and to survive. Some people have taken the “functions like” to mean that the earth is a living organism rather than just a physical thing that supports life.

Such a view fits in well with the views of many environmentalists who can then claim that environmental problems such as pollution are like diseases harming the health of this living organism. This may or may not be true, but the most important result of the idea of the earth acting as a single unitary system, as put forward in the Gaia hypothesis, is the strengthening of the understanding of the connectedness of all things on our planet. And also the dire impact that man has on global processes.

The Gaia hypothesis was first formulated in the mid-1960s by James Lovelock in collaboration with the microbiologist Lynn Margulis. In 1979 Lovelock published a book on Gaia, which is when the idea really became popular. Inherent in Lovelock’s idea is the fact that the living biosphere, the atmosphere, the mineral lithosphere and the hydrosphere seem to work together to maintain a homeostatic condition. ‘Homeostasis’ is a biological term describing how life processes maintain an internal balance, an equilibrium that keeps the organism alive; these processes insure stable temperature, pH, electrochemical balance, energy flows, etc, without all of which the organism would die. The oceans and rivers can be seen as the earth’s blood, the atmosphere is the earth’s lungs, the land is the earth’s bones, and the living organisms are the earth’s senses and organelles.

The key point here is the claim that the earth, powered by energy from the sun, acts as a single system made up of self-regulating physical, chemical, geological, and biological processes and forces, all working together to maintain a unified whole. And if any of those processes drastically alter, the whole will suffer and perhaps die.

The way Lovelock came to develop the hypothesis helps understanding the hypothesis itself. He was part of a NASA team formed in 1965 to search for life on other planets. His job was to design tools capable of detecting the presence of life, for example simple instruments that could be sent on a spacecraft to Mars. This is not as easy as it sounds, since we have no idea what to look for: any life forms on Mars may be very, very different from those we are used to on earth.

Lovelock came up with the idea that if any gases were found in an atmosphere of a dead planet, they would be in chemical equilibrium, that is, all chemical reactions that could have happened would have happened and the gases of the atmosphere would be relatively inert or non-reactive. However if life existed on that planet, the gases would not be in balance since bio-chemical reactions would be going on, using, creating and combining those gases. These reactive gases could be tested, and if found would prove that life existed on that planet.

This stems from the fact that the most general characteristic of life is that it takes in energy and matter and discards waste products. Assuming that organisms use their planet’s atmosphere (as they do on earth) as both a source for useful gases and a dump for waste gases, such a gas exchange would be detectable as a chemical signature in the other planet’s atmosphere, which could be seen using common scientific techniques designed to study the chemical composition of distant objects.

For example, when scientists studied the atmospheric gases present on Mars or Venus, they saw that they were 95% carbon dioxide, a stable non-reactive gas. These planets were chemically dead; all the reactions that were going to take place had already done so. On earth, however, they saw that the atmosphere was an unstable mixture of many gases. The earth was 77% nitrogen, 21% oxygen, and a relatively large amount was methane. Instability means gases like methane and oxygen, which react with each other very easily, are both present and have been so for a long time.

How was this ‘stable’ instability possible? To Lovelock this suggested some form of regulation of the planet’s atmosphere. He initially suggested that life itself maintained the composition of the atmosphere, but then went on to include the whole system of climate, rocks, air and oceans as a self-regulating process.

He noted that about 3 billion years ago, bacteria and photosynthetic algae, the precursors of modern plants, started to remove carbon dioxide from the atmosphere, producing oxygen as a waste product. Over enormous time periods, this process changed the chemical content of the atmosphere to the point where organisms began to suffer from too little carbon dioxide. Then animals evolved that used the oxygen produced by plants and gave off carbon dioxide, which plants can use. Where the output of one thing is used as input by another, whose output is, in turn, used by the first forming a cycle, the process is known as feedback loop. There are a large number of such loops present on earth, mirroring cycles found in living organisms.

The way Gaia works can be made more evident by taking a detailed look at just how this carbon dioxide cycle actually functions, involving not just plants and animals but rocks and oceans. Volcanoes constantly produce massive quantities of carbon dioxide. Since carbon dioxide gas tends to warm the planet, if left to accumulate it would soon make the earth too hot for life. Yet, while plants and animals take in and expel carbon dioxide through life processes such as photosynthesis, respiration and decay, the total amount of carbon dioxide remains the same. How does this happen?

One process by which carbon dioxide is removed from the atmosphere is rock-weathering, where rainwater and carbon dioxide combine with rocks to form carbonates. Lovelock and Margulis discovered that the process is greatly accelerated by the presence of living soil bacteria. The carbonates are washed away into the ocean, where microscopic algae then use them to make tiny shells. When the algae die, their shells sink to the bottom of the ocean, forming limestone sediment rock. These heavy sediments gradually sink until they melt. Eventually, some of the carbon dioxide contained in the limestone will be fed back into the atmosphere through another volcano. Since the soil bacteria are more active in high temperatures, the removal of carbon dioxide is accelerated when the planet is hot. This has the effect of cooling the planet.

These bacteria, along with plants, animals, the rain and the oceans, all seem to be working together in a complex cycle. Such complex cycles combining living and non-living parts of the earth are what make life as we know it possible. And, in turn, life itself makes the physical earth what it is -- a comfortable and hospitable place for life.

-- Manoj Nadkarni

Kids For Change, February 2006